The present invention relates to an electrically depositing drum in a copper foil producing machine for producing copper foil.
Many approaches and improvements have conventionally been made for electrically depositing and forming copper foil having a uniform thickness and a uniform smooth surface on a surface of an electrically depositing drum. In particular, conductivity of the top skin and conductivity and anti-corrosion property of outer circumferential plates of the top skin and an inner drum are improved to make it possible to produce excellent copper foil.
The anti-corrosion problem has recently been solved to some extent by the following steps. Namely, a titanium plate that is superior in anti-corrosion property to electrolyte is used as a top skin. This top skin is bonded on the surface of the inner drum. A titanium electrically depositing drum for forming copper foil having a uniform thickness and a uniform smooth surface on the outer circumferential surface of the titanium plate is used.
In this titanium electrically depositing drum, in general, the titanium plate is bonded on an outer circumferential portion of the inner drum made of soft steel or stainless steel. The copper foil is produced on the outer circumferential surface of the titanium plate by causing current to flow from the titanium plate to the inner drum through the outer circumferential portion. However, the conventional titanium electrically depositing drum suffers from the following problems concerning the conductivity.
i) Unless the contact and intimate bond between the titanium plate and the inner drum are sufficient, a local electric supply trouble occurs.
ii) As the inner drum is gradually corroded by the electrolyte, oxidized scales are formed on the inner drum. For this reason, the conductivity is locally deteriorated.
iii) In the case where the inner drum is made of iron system material, even if an expensive top skin like titanium is coated, when rust is generated on the inner drum, the conductivity of the titanium top skin is deteriorated to thereby offset the superiority of the titanium.
Accordingly, owing to the above-described problems concerning the conductivity, in the conventional titanium electrically depositing drum, there is a fear that a color change caused by the non-uniformity of the thickness of the copper foil, the abnormal precipitation, local heat, i.e., a so-called hot spot would occur. In order to enhance the productivity and the quality of the product, it is necessary to improve the conductivity.